Voltage contrast inspection of deep trench isolation

ABSTRACT

A method including forming a first test structure and a second test structure in electrical contact with an inner buried plate and an outer buried plate, respectively, where the first and second test structures each comprise a deep trench filled with a conductive material, and measuring the voltage of the inner buried plate and the outer buried plate immediately after the formation of a deep trench isolation structure, where the inner buried plate and the outer buried plate are positioned on opposite sides of the deep trench isolation structure.

BACKGROUND

1. Field of the Invention

The present invention generally relates to integrated circuits, and moreparticularly to testing the integrity of deep trench isolationstructures.

2. Background of Invention

Embedded dynamic random access memory (eDRAM) is a critical part ofmodern semiconductor technologies. This memory may require about onethird the space of static random access memory (SRAM) because each bitonly requires one transistor that accesses a capacitor. There existmultiple techniques by which to implement a capacitor in an eDRAMdevice. One way to build the capacitor may be to etch a deep trench in asemiconductor-on-insulator (SOI) substrate and then fill the deep trenchwith a node dielectric and an inner electrode. The structure may beknown as a deep trench capacitor. In such a structure, a layer ofconductive material below the buried dielectric layer of the SOIsubstrate forms a buried plate of the capacitor. The buried plate mayalso be referred to as a cathode, and may generally be doped silicon.The inner electrode formed within the deep trench is the top plate oranode of the capacitor. The buried plate and the top plate may generallybe separated by the node dielectric.

The buried plate, or cathode, for all deep trench capacitors formed in asingle SOI substrate may be electrically connected unless otherwiseintentionally isolated. One method by which to isolate the buried plateof one deep trench capacitor from the buried plate of another deeptrench capacitor may be to create an isolation device extending from atop surface of the SOI substrate to below the buried plate. In somecases the isolation device may completely surround one or more deeptrench capacitors separating them from the rest of the chip. Such anisolation device may commonly be referred to as a deep trench moat(DTMoat).

It may be advantageous to test the integrity of the isolation device toensure the reliability of the semiconductors devices relying on itselectrical isolation properties.

SUMMARY

According to one embodiment of the present invention, a method isprovided. The method may include forming a first test structure and asecond test structure in electrical contact with an inner buried plateand an outer buried plate, respectively, where the first and second teststructures each include a deep trench filled with a conductive material,and measuring the voltage of the inner buried plate and the outer buriedplate immediately after the formation of a deep trench isolationstructure, where the inner buried plate and the outer buried plate arepositioned on opposite sides of the deep trench isolation structure.

According another exemplary embodiment, a method is provided. The methodmay include providing a semiconductor-on-insulator (SOI) substratehaving a buried dielectric layer located above a buried plate, forming adeep trench isolation structure in the SOI substrate having a first nodedielectric and a first inner electrode, where the deep trench isolationstructure electrically isolates an inner buried plate located on oneside of the deep trench isolation structure from an outer buried platelocated on an opposite side of the deep trench isolation structure, andforming a deep trench capacitor in the SOI substrate having a secondnode dielectric and a second inner electrode. The method may furtherinclude forming a first test structure and a second test structure inthe SOI substrate and on opposite sides of the deep trench isolationstructure, the first and second test structures having a third nodedielectric and a third inner electrode, where the first test structureand the second test structure are similar in size and shape, and have adifferent width than the deep trench capacitor, etching the third nodedielectric and the third inner electrode of the first and second teststructures to a first depth below the buried dielectric layer, etchingthe second node dielectric and the second inner electrode of the deeptrench capacitor to a second depth above the buried plate and within theburied dielectric layer, and etching the first node dielectric and thefirst inner electrode to a third depth above the buried plate and withinthe buried dielectric layer, where the first depth is deeper than thesecond depth.

According another exemplary embodiment, a method is provided. The methodmay include a semiconductor-on-insulator (SOI) substrate having a burieddielectric layer located above a buried plate, a deep trench isolationstructure extending into the SOI substrate having a first nodedielectric and a first inner electrode, and being substantially filledwith a first conductive material isolated from the buried plate, wherethe deep trench isolation structure electrically isolates an innerburied plate located on one side of the deep trench isolation structurefrom an outer buried plate located on an opposite side of the deeptrench isolation trench structure, a deep trench capacitor extendinginto the SOI substrate having a second node dielectric and a secondinner electrode, and being substantially filled with a second conductivematerial isolated from the buried plate, and a first test structure anda second test structure extending into the SOI substrate having a thirdnode dielectric and a third inner electrode, and being substantiallyfilled with a third conductive material, where the third conductivematerial of the first test structure is in electrical contact with theinner buried plate and the first conductive material of the second teststructure is in electrical contact with the outer buried plate, andwhere the first test structure and the second test structure are similarin size and shape, and have a different width than the deep trenchcapacitor.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

The following detailed description, given by way of example and notintended to limit the invention solely thereto, will best be appreciatedin conjunction with the accompanying drawings, in which:

FIG. 1 depicts a top view of a semiconductor structure according to anexemplary embodiment.

FIGS. 2-9 illustrate the steps of a method of forming the semiconductorstructure according to an exemplary embodiment.

FIG. 2 depicts the formation of multiple deep trench structuresaccording to an exemplary embodiment.

FIG. 3 depicts the deposition of a node dielectric and a metallic lineraccording to an exemplary embodiment.

FIG. 4 depicts the deposition of an inner electrode according to anexemplary embodiment.

FIG. 5 depicts the removal of a portion of the node dielectric, metallicliner, and the inner electrode according to an exemplary embodiment.

FIG. 6 depicts the removal of another portion of the node dielectric,the metallic liner, and the inner electrode according to an exemplaryembodiment.

FIG. 7 depicts the deposition of a conductive material according to anexemplary embodiment.

FIG. 8 depicts a section view of FIG. 7 according to an exemplaryembodiment.

FIG. 9 depicts a section view of FIG. 7 according to an exemplaryembodiment.

The drawings are not necessarily to scale. The drawings are merelyschematic representations, not intended to portray specific parametersof the invention. The drawings are intended to depict only typicalembodiments of the invention. In the drawings, like numbering representslike elements.

DETAILED DESCRIPTION

Detailed embodiments of the claimed structures and methods are disclosedherein; however, it can be understood that the disclosed embodiments aremerely illustrative of the claimed structures and methods that may beembodied in various forms. This invention may, however, be embodied inmany different forms and should not be construed as limited to theexemplary embodiments set forth herein. Rather, these exemplaryembodiments are provided so that this disclosure will be thorough andcomplete and will fully convey the scope of this invention to thoseskilled in the art. In the description, details of well-known featuresand techniques may be omitted to avoid unnecessarily obscuring thepresented embodiments.

The invention relates to voltage contrast (VC) inspection, and moreparticularly, VC inspection used to test the functionality and integrityof a deep trench isolation structure. In a preferred embodiment, the VCinspection may be carried out on a structure in which voltage readingsbased on a voltage contrast signal from opposite sides of the deeptrench isolation structure may be compared and contrasted. Comparison ofthese voltage measurements may yield a prediction as to whether the deeptrench isolation structure is functioning properly, and preventing theflow of electrical current. Typically, VC inspection cannot be initiateduntil a device contact layer or a first metallization layer are formed.These layers were the only method by which to make electrical contact tothe buried plate in order to conduct VC inspection. The followingdisclosure will discuss a structure and method by which to conduct VCinspection shortly after the isolation structure is formed. Testing theisolation structure earlier in the fabrication process may preventunnecessary fabrication time and cost in the event the isolationstructure fails the test. The detailed description below will firstreview the formation of the structure followed by a detailed descriptionof the VC inspection procedure.

Referring now to FIG. 1, a structure 100 is shown having a firstplurality of test structures 104 a, a second plurality of teststructures 104 b, a plurality of deep trench capacitors 106, a deeptrench isolation structure 108 (DT isolation structure 108), and aground structure 110 formed in a substrate 102. The first and secondtest structures 104 a, 104 b may be integrated into typical fabricationand process flows in order to conduct VC inspection testing. The VCinspection testing may be conducted to determine the integrity of the DTisolation structure 108. The DT isolation structure 108 may be designedto electrically isolate semiconductor devices formed on opposite sidesof the DT isolation structure 108. In one embodiment, as depicted in thefigure, the DT isolation structure 108 may include a deep trenchisolation moat surrounding one or more semiconductor devices. In thepresent embodiment, the deep trench isolation moat may electricallyisolate semiconductor devices inside the moat from semiconductor devicesoutside the moat.

The first and second test structures 104 a, 104 b may be constructedsolely for the purpose of conducting the VC inspection testing. The deeptrench capacitors 106 may be formed as components in a semiconductordevice, for example, a deep trench capacitor used in an embedded DRAMmemory cell. The first and second test structures 104 a, 104 b, the deeptrench capacitors 106, and the DT isolation structure 108 may preferablybe simultaneously formed during typical process flows without the needfor additional steps. However, the first and second test structures 104a, 104 b, the deep trench capacitors 106, and the DT isolation structure108 may alternatively be formed by individual processes. The VCinspection testing sequence will be described in greater detail below,after a detailed description of forming the structure 100 is presented.It should be noted that only two test structures may be needed toconduct the VC inspection testing, however multiple test structures, forexample the first and second test structures 104 a, 104 b, may befabricated on both sides of the DT isolation structure 108 forredundancy purposes. Furthermore, the first and second test structures104 a, 104 b, the deep trench capacitors 106, and the DT isolationstructure 108 may be fabricated in any suitable configuration andlocation relative to one another, so long as, at least one teststructure, for example the first test structure 104 a, may be positionedon one side of the DT isolation structure 108 and at least one teststructure, for example the second test structure 104 b, may bepositioned on an opposite side of the DT isolation structure 108.

Referring now to FIGS. 2-7, exemplary process steps of forming thestructure 100 in accordance with one embodiment of the present inventionare shown, and will now be described in greater detail below. It shouldbe noted that FIGS. 2-7 all represent a cross section view, section A-A,of the structure 100 depicted in FIG. 1. It should also be noted thatwhile this description may refer to some components of the structure 100in the singular tense, more than one component may be depictedthroughout the figures and like components are labeled with likenumerals. For example, only two test structures 104 a, 104 b and onedeep trench capacitor 106 are depicted in the following figures forillustrative purposes only. The process steps described below withreference to FIGS. 2-7 may apply to the entire structure 100 as depictedin FIG. 1.

Referring now to FIG. 2, a cross section view, section A-A, of thestructure 100 is shown at an intermediate step during the process flow.At this step of fabrication, and as described above, the structure 100may include the first plurality of test structures 104 a, the secondplurality of test structures 104 b, the plurality of deep trenchcapacitor 106, and the DT isolation structure 108; however, FIG. 2depicts a cross section view including only two test structures 104 a,104 b, a single deep trench capacitor 106, and the DT isolationstructure 108.

Generally, the substrate 102 of the structure 100 may be asemiconductor-on-insulator (SOI) substrate. The SOI substrate employedin the present invention may include a base substrate 114, a buriedplate 116 formed on top of the base substrate 114, a buried dielectriclayer 118 formed on top of the buried plate 116, and a SOI layer 120formed on top of the buried dielectric layer 118. The buried dielectriclayer 118 may isolate the SOI layer 120 from the buried plate 116. Also,a pad layer 112 may be formed on top of the SOI layer 120.

The base substrate 114 may be made from any of several knownsemiconductor materials such as, for example, silicon, germanium,silicon-germanium alloy, silicon carbide, silicon-germanium carbidealloy, and compound (e.g. III-V and II-VI) semiconductor materials.Non-limiting examples of compound semiconductor materials includegallium arsenide, indium arsenide, and indium phosphide. Typically thebase substrate 114 may be about, but is not limited to, several hundredmicrons thick. For example, the base substrate 114 may include athickness ranging from 0.5 mm to about 1.5 mm.

The buried plate 116 may be made from any suitable conductive material,for example, a doped semiconductor material. In one embodiment, theburied plate 116 may include any material listed above for the basesubstrate 114 that which may be doped with either p-type dopants orn-type dopants to induce conductive properties. In one embodiment, theburied plate 116 may have a vertical thickness ranging from about 5 nmto about 100 nm, and more typically from about 10 nm to about 50 nm,although lesser and greater thicknesses may be explicitly contemplated.In the present embodiment, the buried plate 116 may include an innerburied plate 116 a and an outer buried plate 116 b. The inner buriedplate 116 a may include a portion of the buried plate 116 located withinthe DT isolation structure 108, and the outer buried plate 116 b mayinclude a portion of the buried plate 116 located outside the DTisolation structure 108.

The buried dielectric layer 118 may be formed from any of several knowndielectric materials. Non-limiting examples include, for example,oxides, nitrides and oxynitrides of silicon. Oxides, nitrides andoxynitrides of other elements are also envisioned. In addition, theburied dielectric layer 118 may include crystalline or non-crystallinedielectric material. Moreover, the buried dielectric layer 118 may beformed using any of several known methods. Non-limiting examples includeion implantation methods, thermal or plasma oxidation or nitridationmethods, chemical vapor deposition methods and physical vapor depositionmethods. In one embodiment, the buried dielectric layer 118 may be about150 nm thick. Alternatively, the buried dielectric layer 118 may includea thickness ranging from about 10 nm to about 500 nm.

The SOI layer 120 may include any of the several semiconductor materialsincluded in the base substrate 114. In general, the base substrate 114and the SOI layer 120 may include either identical or differentsemiconducting materials with respect to chemical composition, dopantconcentration and crystallographic orientation. In one particularembodiment of the present invention, the base substrate 114 and the SOIlayer 120 may include semiconducting materials that include at leastdifferent crystallographic orientations. Typically the base substrate114 or the SOI layer 120 may include a {110} crystallographicorientation and the other of the base substrate 114 or the SOI layer 120may include a {100} crystallographic orientation. Typically, the SOIlayer 120 may include a thickness ranging from about 5 nm to about 100nm. Methods for forming the SOI layer 120 are well known in the art.Non-limiting examples include SIMOX (Separation by Implantation ofOxygen), wafer bonding, and ELTRAN® (Epitaxial Layer TRANsfer).

The pad layer 112 may include an insulating material such as, forexample, silicon nitride. The pad layer 112 may be formed usingconventional deposition methods, for example, low-pressure chemicalvapor deposition (LPCVD). The pad layer 112 may have a thickness rangingfrom about 10 nm to about 500 nm. In one particular embodiment, the padlayer 112 may be about 100 nm thick. Optionally, a thin (2 nm to 10 nm,preferably 5 nm) thermal oxide layer (not shown) may be formed on theSOI layer 120 prior to forming the pad layer 112. Typically, the padlayer 112 may be used to protect the substrate 102 during subsequentprocessing operations.

With continued reference to FIG. 2, a location may be identified and amask layer (not shown) of a suitable masking material may be depositedon the pad layer 112 and patterned using a conventionalphotolithographic techniques. The mask layer may include any suitablemasking material such as photoresist or hardmask, for example, silicondioxide. A first opening 103 a and a second opening 103 b may be formedby etching into the substrate 102 as illustrated by the figure. Thefirst and second openings 103 a, 103 b can be formed using, for example,an anisotropic dry etch technique, such as reactive ion etching (RIE).The mask layer may be removed after the first and second openings 103 a,103 b is formed, or alternatively, in a later process. A similar etchingtechnique as described above may subsequently be used to form a thirdopening 105 and a fourth opening 107. It should be noted that the firstand second openings 103 a, 103 b may be further processed tosubsequently form the test structures 104 a, 104 b, the third opening105 may be further processed to subsequently form the deep trenchcapacitor 106, and the fourth opening 107 may be further processed tosubsequently form the DT isolation structure 108.

Each of the openings 103 a, 103 b, 105, 107 may have a different size,shape, and depth, while noting that the first and second openings 103 a,103 b being substantially similar. Generally, the first and secondopenings 103 a, 103 b and the third opening 105 may have similar depths,and may extend from a top surface of the SOI layer 120 down to apredetermined location below the buried dielectric layer 118 and abovethe base substrate 114. In one embodiment, the first and second openings103 a, 103 b and the third opening 105 may have a depth ranging fromabout 200 nm to about 800 nm, with a depth of 500 nm being more typical.It should be noted that the preferred recess depth of the first andsecond openings 103 a, 103 b depends on the thickness of the buriedplate 116, the buried dielectric layer 118, and the SOI layer 120. Thefirst and second openings 103 a, 103 b and the third opening 105 mayalso be similar in shape, but have different widths. The first andsecond openings 103 a, 103 b may have a smaller width than the thirdopening 105. In one embodiment, the third opening 105 may have a widthranging from about 40 nm to about 120 nm, with a width of 80 nm beingmost typical. The width of the first and second openings 103 a, 103 bmay be adjusted based on the desired result of future processingtechniques as described in greater detail below with reference to FIG. 5while generally maintaining a width less than the width of the thirdopening 105. The fourth opening 107 may generally be deeper and widerthan either the first and second openings 103 a, 103 b or the thirdopening 105. The fourth opening 107 may extend from the top surface ofthe SOI layer 120 down to a predetermined location within the basesubstrate 114 below the buried plate 116. The fourth opening 107 mayextend into the base substrate 114 to effectively isolate semiconductordevices subsequently formed on opposite sides of the fourth opening 107,or opposite sides of the DT isolation structure 108. In one embodiment,the fourth opening 107 may have a width ranging from about 200 nm toabout 300 nm, with a width of 250 nm being most typical.

Now referring to FIG. 3, a node dielectric 122 and a metallic liner 124,may be conformally deposited within the openings 103 a, 103 b, 105, 107.The node dielectric 122 and the metallic liner 124 may or may not derequired in all the openings, however, the node dielectric 122 and themetallic liner 124 may be deposited in all the openings 103 a, 103 b,105, 107 to minimize process steps and maintain current process flows.

The node dielectric 122 may include, for example, oxides, nitrides,oxynitrides and/or high-k materials, and can be formed within theopenings by any suitable process such as thermal oxidation, thermalnitridation, atomic layer deposition (ALD), chemical vapor deposition(CVD). In one embodiment, the node dielectric 122 may comprise a high-kmaterial having a dielectric constant greater than the dielectricconstant of silicon nitride, which is about 7.5. Exemplary high-kmaterials may include HfO₂, ZrO₂, La₂O₃, Al₂O₃, TiO₂, SrTiO₃, LaAlO₃,Y₂O₃, HfO_(x)N_(y), ZrO_(x)N_(y), La₂O_(x)N_(y), Al₂O_(x)N_(y),TiO_(x)N_(y), SrTiO_(x)N_(y), LaAlO_(x)N_(y), Y₂O_(x)N_(y), a silicatethereof, and an alloy thereof. Each value of x may independently rangefrom about 0.5 to about 3 and each value of y may independently rangefrom 0 to about 2. The node dielectric 122 may have a thickness rangingfrom about 8 nm to about 12 nm, although a thickness of the nodedielectric 122 less than 8 nm or greater than 12 nm may be conceived.Preferably, the node dielectric 122 may have a thickness of about 10 nm.

The metallic liner 124 may then be deposited on the surface of the nodedielectric 122. The metallic liner 124 may include any suitableconductive material, including but not limited to, doped polycrystallineor amorphous silicon, germanium, silicon germanium, a metal (e.g.,tungsten, titanium, tantalum, ruthenium, zirconium), a conductingmetallic compound material (e.g., tantalum nitride, titanium nitride,tungsten silicide, tungsten nitride, titanium nitride, tantalumnitride), carbon nanotube, conductive carbon, or any suitablecombination of these materials. The metallic liner 124 can be depositedby any suitable method, including but not limited to, atomic layerdeposition (ALD), chemical vapor deposition (CVD), low-pressure chemicalvapor deposition (LPCVD), ultrahigh vacuum chemical vapor deposition(UHVCVD), metalorganic chemical vapor deposition (MOCVD), physical vapordeposition, sputtering, plating, evaporation, spin-on-coating, ion beamdeposition, electron beam deposition, laser assisted deposition, andchemical solution deposition. In one particular embodiment, the metallicliner 124 may include doped polysilicon deposited by LPCVD. The metallicliner 124 may have a thickness ranging from about 8 nm to about 13 nm,although a thickness of the metallic liner 124 less than 8 nm or greaterthan 13 nm may be conceived. Preferably, the metallic liner 124 may havea thickness of about 10.5 nm.

Referring now to FIG. 4, an inner electrode 126 may be formed bydepositing any suitable conductive material on the inner walls of themetallic liner 124. The inner electrode 126 may be a doped semiconductormaterial or a metal. If the inner electrode 126 is a doped semiconductormaterial, the doped semiconductor material may include any materiallisted above for the base substrate 114. The dopants may be a p-typedopant or an n-type dopant. The doped semiconductor material may bedeposited by chemical vapor deposition such as low pressure chemicalvapor deposition (LPCVD). In one embodiment, the inner electrode 126 mayinclude amorphous silicon deposited by LPCVD

If the inner electrode 126 is an elemental metal, exemplary elementalmetals may include Ta, Ti, Co, and W. Alternatively, the inner electrode126 may be a conductive metallic alloy, and exemplary conductivemetallic alloys may include a mixture of elemental metals, a conductivemetallic nitride such as TiN, ZrN, HfN, VN, NbN, TaN, WN, TiAlN, TaCN,and an alloy thereof. The inner electrode 126 may be formed by knownsuitable deposition techniques, for example, chemical vapor deposition(CVD), physical vapor deposition (PVD), or atomic layer deposition(ALD). The node dielectric 122 may serve as an insulating barrier toprevent a short circuit between the buried plate 116 and the metallicliner 124 or the inner electrode 126. In one embodiment, the metallicliner 124 may be omitted, and the inner electrode 126 may be depositeddirectly on top of the node dielectric 122.

In one embodiment, the openings 103 a, 103 b, 105, 107 (shown in FIG. 2)may each be fabricated individually and each having different fillcompositions. The first and second openings 103 a, 103 b may besubstantially filled with any suitable conductive material. The thirdopening 105 may be filled with a node dielectric, a metallic liner, andan inner electrode as described previously above. The fourth opening 107may be substantially filled with any known insulative material, forexample a dielectric.

With continued reference to FIG. 4, the test structures 104 a, 104 b,the deep trench capacitor 106, and the DT isolation structure 108 may bedepicted at an intermediate step of fabrication. It should be noted thatthere exists a direct correlation between the size, shape, and depth ofthe test structures 104 a, 104 b, the deep trench capacitor 106, and theDT isolation structure 108, and the first and second openings 103 a, 103b, the third opening 105, and the fourth opening 107, respectively.Thus, the test structures 104 a, 104 b may generally be smaller than thedeep trench capacitor 106, and the DT isolation structure 108 maygenerally be larger than both the test structures 104 a, 104 b and thedeep trench capacitor 106.

Referring now to FIG. 5, a first recess etching technique (“the firstrecess etch”) may be used to recess the node dielectric 122, themetallic liner 124, and the inner electrode 126. Any suitable chemicaletching technique can be used for the first recess etch. In oneembodiment, for example, a reactive ion etch (RIE) technique usingC_(x)Fl_(y) chemistries may be used to recess the node dielectric 122,the metallic liner 124, and the inner electrode 126. The first recessetch may be selective to the pad layer 112 and etch or remove only thenode dielectric 122, the metallic liner 124, and the inner electrode126. The first recess etch may result in new openings 128 a, 128 b, 130,132. It should be noted there may exists a direct relationship betweenthe openings 103 a, 103 b, 105, 107 and the openings 128 a, 128 b, 130,132, respectively. It should also be noted that, like the first andsecond openings 103 a, 103 b, the openings 128 a, 128 b may be similarin size.

The particular etching technique used for the first recess etch may becalibrated to produce an inverse RIE lag affect, in which there exists acorrelation between the feature width and the recess depth. Inverse RIElag, as is known in the art, produces a faster etch rate in narroweropenings (higher aspect ratios) than in openings having larger widths(lower aspect ratios). Inverse RIE lag may be induced under anyconditions characterized by high polymerization and high wafer self-biasvoltages. In one embodiment, conditions characterized by highpolymerization, may include general chemistries such as CxHyFz(Carbon-Hydrogen-Fluorine) with high oxide-to-nitride selectivity (wherethe blanket etch rate ratios is greater than approximately 20:1). Inanother embodiment, conditions characterized by high polymerization, mayinclude general chemistries such as O2 (oxygen), a dilutant, and onemore of: C4F6, C5F8, or C4F8. In this case, the dilutant may be, forexample, Argon (Ar). High wafer self-bias voltages may, for example, bevoltages greater than approximately 500 volts. While specific conditionsfor facilitating inverse RIE lag are described herein, those conditionsare merely illustrative. Inverse RIE lag may be induced under otherconditions not specifically described herein.

In the present embodiment, for example, the openings 128 a, 128 b mayhave a larger recess depth than the opening 130, because the openings128 a, 128 b may have a smaller width than the opening 130. The openings128 a, 128 b may have a recess depth (a) and the opening 130 may have arecess depth (b), and therefore the recess depth (a), of the openings128 a, 128 b, may be larger than the recess depth (b), of the opening130. Similarly, for example, both the openings 128 a, 128 b and theopening 130 may each have a recess depth considerably deeper than theopening 132, because the opening 132 may be considerably larger thanboth the openings 128 a, 128 b and the opening 130. The opening 132 mayhave a recess depth (c), and therefore the recess depth (a), of theopenings 128 a, 128 b, and the recess depth (b), of the opening 130, mayeach be larger than the recess depth (c), of the opening 132.Ultimately, the openings 128 a, 128 b, 130, 132 may each have adifferent recess depth due to their different widths, while noting thatthe openings 128 a, 128 b may be substantially similar.

With continued reference to FIG. 5, as described above, different sizefeatures may each have a different recess depth as a result of the firstrecess etch. As described above, the openings 128 a, 128 b, 130, 132 maycorrespond to the test structures 104 a, 104 b, the deep trenchcapacitor 106, and the DT isolation structure 108, respectively. In oneembodiment, the opening 130 may be recessed to a predetermined depthwithin the buried dialectic layer 118 to ensure electrical isolationbetween the metallic liner 124, and the inner buried plate 116 a. Theelectrical isolation may be achieve by ensuring the node dielectric 122remains between the metallic liner 124, and the inner buried plate 116a. Risk of an electrical short may be present should the opening 130 berecessed to a level below the buried dielectric layer 118. Suchelectrical isolation may be preferred in order to form the correspondingfeature to the opening 130, the deep trench capacitor 106.

In one embodiment, the openings 128 a, 128 b may preferably be recessedto a predetermined depth below the buried dialectic layer 118 to exposesome portion of the inner and outer buried plates 116 a, 116 b. Apreferred electrical connection may be made to the exposed portion ofthe inner and outer buried plates 116 a, 116 b as described in greaterdetail below with reference to FIG. 7. As described above, the preferredrecess depth below the buried dielectric layer 118 may be achieved bycarefully adjusting the width of the opening.

In one embodiment, similar results may be achieved by applying a knownRIE lag technique to a similar structure where the test structures 104a, 104 b may be larger in width than the deep trench capacitor 106. Insuch an instance and under the known principles of RIE lag, the largerfeatures, for example the test structures 104 a, 104 b, may etch fasterthan the smaller structures, for example, the deep trench capacitor 106.The DT isolation structure 108 may still be considerably larger thaneither the test structures 104 a, 104 b or the deep trench capacitor106.

Referring now to FIG. 6, a second recess etching technique (“the secondrecess etch”) may be used to recess further the node dielectric 122, themetallic liner 124, and the inner electrode 126. Known etchingtechniques may be used for the second recess etch, for example a RIEtechnique. The particular etch rate of the technique used may be finetuned to achieve desired results. For example, the second recess etchmay preferably recess the node dielectric 122, the metallic liner 124,and the inner electrode 126 within the opening 132 to a location withinthe buried dielectric layer 118. Like the first recess etch, the secondrecess etch may be selective to the pad layer 112 and etch or removeonly the node dielectric 122, the metallic liner 124, and the innerelectrode 126. Also, the second etch may primarily recess the nodedielectric 122, the metallic liner 124, and the conductive material 126within the opening 132, while recessing little if any of the nodedielectric 122, the metallic liner 124, and the conductive material 126within the openings 128 a, 128 b, 130. In one embodiment, a RIEtechnique using a combination of C_(x)Fl_(y) and Ar chemistries may beused to further recess the node dielectric 122, the metallic liner 124,and the inner electrode 126. Typical known principles of RIE lag may beapplied to achieve the desired recess depths.

Referring now to FIG. 7, a conductive fill material 134 may be depositedin, and substantially fill, the openings 128 a, 128 b, 130, 132. Theconductive fill 134 may include any suitable conductive material, forexample, amorphous silicon. It may be an advantage of the presentembodiment that electrical contact is made with the inner and outerburied plates 116 a, 116 b via the conductive fill 134. The desiredelectrical connection may be formed within the test structures 104 a,104 b where the conductive material 134 comes in direct contact with theinner and outer buried plates 116 a, 116 b. See also FIG. 9. Also, asmentioned above, it may be an advantage of the present embodiment thatelectrical isolation be maintained between the inner buried plate 116 a,and the metallic liner 124 of the deep trench capacitor 106. See FIG. 8.This electrical isolation may be provided by the dielectric liner 122.The electrical connection to the inner and outer buried plates 116 a,116 b, made at the test structures 104 a, 104 b, may be used to measurethe voltage of the inner and outer buried plates 116 a, 116 b shortlyafter the formation of the DT isolation structure 108. Morespecifically, the voltage of the inner buried plate 116 a may becompared with the voltage of the outer buried plate 116 b to assess andensure the functionality and integrity of the DT isolation structure108. This testing procedure may be described in greater detail below.

With continued reference to FIG. 7, the structure 100 is depicted at anintermediate step of fabrication. At this step, the structure 100 mayinclude, as shown in FIG. 6, the test structures 104 a, 104 b, the deeptrench capacitor 106, and the DT isolation structure 108. The teststructures 104 a, 104 b may include the node dialectic 122, the metallicliner 124, and the inner electrode 126 recessed to a level below theburied dielectric layer 118. The deep trench capacitor 106 may includethe node dialectic 122, the metallic liner 124, and the inner electrode126 recessed to a level within the buried dielectric layer 118. The DTisolation structure 108 may include the node dialectic 122, the metallicliner 124, and the inner electrode 126 recessed to a level within theburied dielectric layer 118. The test structures 104 a, 104 b, the deeptrench capacitor 106, and the DT isolation structure 108 all have theconductive fill 134 which may substantially fill each element. In thecase of the test structures 104 a, 104 b the conductive fill 134 may bein electrical contact with the buried plates 116 a, 116 b, respectively.See also FIG. 9. In the case of the deep trench capacitor 106 and the DTisolation structure 108 the conductive fill 134 may remain electricallyisolated from the buried plates 116 a, 116 b. See also FIG. 8.

Immediately following the formation of the test structures 104 a, 104 b,the deep trench capacitor 106, and the DT isolation structure 108, asdepicted in FIG. 7, a VC inspection testing sequence (“the testingsequence”) may be used to test the functionality and integrity of the DTisolation structure 108. Typically, a contact level and a metallizationlevel are required to measure the voltage of the inner and outer buriedplates 116 a, 116 b in order to test the DT isolation structure 108. Thetime and expense of fabricating these additional levels may be fornothing should the DT isolation structure 108 fail the testing sequence.The testing sequence may be carried out on the structure 100immediately, or shortly, after the formation of the DT isolationstructure 108. The ability to do so may save fabrication time and costsbecause the additional contact and metallization levels may no longer beneeded to measure the voltage of the inner and outer buried plates 116a, 116 b. A voltage measurement of the inner and outer buried plates 116a, 116 b may be conducted through the test structures 104 a, 104 b. Asdescribed in detail above, the conductive material 134 of the teststructures 104 a, 104 b may be in direct contact with the inner andouter buried plates 116 a, 116 b due to the recess depth of the firstrecess etch, see FIG. 9. Furthermore, it should be noted that the teststructure 104 a may be located within the DT isolation structure 108 andthe test structure 104 b may be located outside the DT isolationstructure 108 in order to obtain voltage measurements of the inner andouter buried plate 116 a, 116 b. See FIG. 1.

The testing sequence may include measuring the voltage of the innerburied plate 116 a, and measuring the voltage of the outer buried plate116 b. The voltage of the inner buried plate 116 a may differ from thevoltage of the outer buried plate 116 b. In one embodiment, the voltagemeasurements may differ by about 1-5 volts. In such cases, it may bedetermined that the DT isolation structure 108 is properly isolating theinner buried plate 116 a from the outer buried plate 116 b. In oneembodiment, the voltage of the inner buried plate 116 a may besubstantially equal to the voltage of the outer buried plate 116 b. Insuch cases, it may be determined that the DT isolation structure 108 isnot properly isolating the inner buried plate 116 a from the outerburied plate 116 b.

The testing sequence may be conducted using any method for VC inspectiontesting known in the art. In one embodiment, for example, an inspectionscanning electron microscope (SEM) may be used to conduct the VCinspection test. In such instances an electron beam (e-beam) may be usedto charge the inner and outer buried plates 116 a, 116 b, through teststructures 104 a, 104 b, and thereby induce voltages. The electronemission of each of the test sites, for example, the test structures 104a, 104 b, is measured to determine the relative voltage between theinner buried plate 116 a and the outer buried plate 116 b. If the DTisolation structure 108 is functioning properly, the inner buried plate116 a may be smaller in area and therefore have a lower capacitance.Both the inner and outer buried plates 116 a, 116 b will charge upthrough the test structures 104 a, 104 b. The inner plate 116 a, willcharge up to a higher voltage than the outer buried plate 116 b becauseof the size difference and resulting difference in capacitance betweenthe inner buried plate 116 a and the outer buried plate 116 b.Therefore, the electron emission may be directly related to howpositively charged the particular test structure is. Under positive modeconditions, in which the wafer surface may be positively charged, thegreater the positive charge of a particular test site the fewerelectrons it may emit. It should be noted that at least one teststructure, for example the test structure 104 a, may form an electricalcontact with the inner buried plate 116 a and at least one teststructure, for example the test structure 104 b, may form and electricalcontact with the outer buried plate 116 b.

If the electron emission measured from the test structure 104 a is thesame as the electron emission measured from the test structure 104 b,then there may be an indication that the DT isolation structure 108 isshorted, and therefore not properly functioning as an isolationstructure. If the electron emission measured from the test structure 104a is different from the electron emission measured from the teststructure 104 b, then there may be an indication that the DT isolationstructure 108 is effectively isolating the inner buried plate 116 a fromthe outer buried plate 116 b. Also, the DT isolation structure 108 maybe connected to the ground structure 110 (shown in FIG. 1). The groundstructure 110 may be connected to a capacitor and function as a virtualground in order to eliminate current flow between the inner and outerburied plates 116 a, 116 b. The bottom of the DT isolation structure 108effectively forms an NFET where the inner and outer buried plates 116 a,116 b may act as the source and drain. This simulated transistorstructure may be forced off by grounding the DT isolation structure 108.A large capacitor may be used to provide the virtual grounding.

The descriptions of the various embodiments of the present inventionhave been presented for purposes of illustration, but are not intendedto be exhaustive or limited to the embodiments disclosed. Manymodifications and variations will be apparent to those of ordinary skillin the art without departing from the scope and spirit of the describedembodiments. The terminology used herein was chosen to best explain theprinciples of the embodiment, the practical application or technicalimprovement over technologies found in the marketplace, or to enableothers of ordinary skill in the art to understand the embodimentsdisclosed herein.

What is claimed is:
 1. A method comprising: forming a first teststructure and a second test structure in electrical contact with aninner buried plate and an outer buried plate, respectively, wherein thefirst and second test structures each comprise a deep trench filled witha conductive material; and measuring the voltage of the inner buriedplate and the outer buried plate immediately after the formation of adeep trench isolation structure, wherein the inner buried plate and theouter buried plate are positioned on opposite sides of the deep trenchisolation structure.
 2. The method of claim 1, further comprising:comparing the voltage measurement of the inner buried plate with thevoltage measurement of the outer buried plate; and determining theintegrity of the deep trench isolation structure based on the voltagemeasurements of the inner buried plate and the outer buried plate. 3.The method of claim 1, wherein measuring the voltage of the inner buriedplate and the outer buried plate comprises using an inspection scanningelectron microscope to detect electron emission.
 4. The method of claim1, wherein the deep trench isolation structure completely surrounds theinner buried plate and electrically isolates the inner buried plate fromthe outer buried plate.
 5. A method comprising: providing asemiconductor-on-insulator (SOI) substrate having a buried dielectriclayer located above a buried plate; forming a deep trench isolationstructure in the SOI substrate having a first node dielectric and afirst inner electrode, wherein the deep trench isolation structureelectrically isolates an inner buried plate located on one side of thedeep trench isolation structure from an outer buried plate located on anopposite side of the deep trench isolation structure; forming a deeptrench capacitor in the SOI substrate having a second node dielectricand a second inner electrode; forming a first test structure and asecond test structure in the SOI substrate and on opposite sides of thedeep trench isolation structure, the first and second test structureshaving a third node dielectric and a third inner electrode, wherein thefirst test structure and the second test structure are similar in sizeand shape, and have a different width than the deep trench capacitor;etching the third node dielectric and the third inner electrode of thefirst and second test structures to a first depth below the burieddielectric layer; etching the second node dielectric and the secondinner electrode of the deep trench capacitor to a second depth above theburied plate and within the buried dielectric layer; and etching thefirst node dielectric and the first inner electrode to a third depthabove the buried plate and within the buried dielectric layer, whereinthe first depth is deeper than the second depth.
 6. The method of claim5, wherein the first and second test structures have a smaller widththan the deep trench capacitor.
 7. The method of claim 5, wherein thefirst and second test structures have a larger width than the deeptrench capacitor.
 8. The method of claim 5, further comprising: fillingthe first and second test structures, the deep trench capacitor, and thedeep trench isolation structure with an electrically conductivematerial, wherein the electrically conductive material associated withthe first and second test structures is in electrical contact with theinner buried plate and the outer buried plate, respectively, and whereinthe electrically conductive material of the deep trench capacitor andthe deep trench isolation structure remains isolated from the buriedplate.
 9. The method of claim 5, wherein the deep trench isolationstructure completely surrounds the inner buried plate and electricallyisolates the inner buried plate from the outer buried plate.
 10. Astructure comprising: a semiconductor-on-insulator (SOI) substratehaving a buried dielectric layer located above a buried plate; a deeptrench isolation structure extending into the SOI substrate having afirst node dielectric and a first inner electrode, and beingsubstantially filled with a first conductive material isolated from theburied plate, wherein the deep trench isolation structure electricallyisolates an inner buried plate located on one side of the deep trenchisolation structure from an outer buried plate located on an oppositeside of the deep trench isolation trench structure; a deep trenchcapacitor extending into the SOI substrate having a second nodedielectric and a second inner electrode, and being substantially filledwith a second conductive material isolated from the buried plate; and afirst test structure and a second test structure extending into the SOIsubstrate having a third node dielectric and a third inner electrode,and being substantially filled with a third conductive material, whereinthe third conductive material of the first test structure is inelectrical contact with the inner buried plate and the first conductivematerial of the second test structure is in electrical contact with theouter buried plate, and wherein the first test structure and the secondtest structure are similar in size and shape, and have a different widththan the deep trench capacitor.
 11. The structure of claim 8, furthercomprising: filling the first, the second, and the third deep trenchstructure with an electrically conductive material, wherein electricallyconductive material associated with the first deep trench structure iselectrically connected to a buried plate corresponding to the first deeptrench structure.
 12. The structure of claim 10, wherein the deep trenchisolation structure completely surrounds the inner buried plate andelectrically isolates the inner buried plate from the outer buriedplate.